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Attenuation artifacts in SPECT: effect of wrap-around lung in 180 degrees cardiac studies
E V Di Bella1, R L Eisner, A B Barclay
1Department of Electrical Engineering, Georgia Institute of Technology, Atlanta, USA.
Unlabelled:
We estimated that in 75%-90% of PET 82Rb patients the left lung appeared to wrap around the anterior aspect of the left ventricle. We used clinical PET 82Rb myocardial perfusion studies as the input to a SPECT computer simulation model to determine if patients with left lung wrap-around displayed consistent artifacts in reconstructed SPECT images. In particular, we sought an explanation for the hot lateral wall seen in SPECT images from normal female and male patients.
Methods:
Attenuated SPECT 201Tl emission data were simulated from a mid-ventricular slice in 10 randomly selected clinical PET 82Rb studies with left lung wrap-around. In these same cases, the influence of left lung wrap-around was removed by assigning the left lung an attenuation coefficient which matched that of the heart. Five randomly selected clinical PET 82Rb studies without left lung wrap-around were also processed with our model.
Results:
In all 10 cases with left lung wrap-around, reconstructed SPECT images showed the hot lateral wall artifact with a mean septal-to-lateral wall count ratio of 0.86. With left lung wrap-around removed in the same 10 patients, reconstructed images did not show hot lateral wall (mean septal-to-lateral wall count ratio = 1.07). The 5 cases without left lung wrap-around did not show hot lateral wall (mean septal-to-lateral wall count ratio = 1.04) and the ratios changed little with the filling of the left lung (mean septal-to-lateral wall count ratio = 1.05).
Conclusion:
Results of our PET-to-SPECT computer simulation model showed that the hot lateral wall artifact found in SPECT myocardial perfusion images was related to the orientation and positions of the left ventricle and the left lung.